If you are looking for a top of the line Z68 motherboard then two of the models you should consider are the ASUS Maximus IV Extreme-Z and Maximus IV Gene-Z. While they share many characteristics you can think of the Extreme-Z as the gaming board because of the four PCIe 16x slots and the Gene-Z as the media motherboard as it sports an HDMI out which the Extreme-Z does not. As well as the difference in output, the Extreme-z has the common Realtek ALC 889 8-Channel High Definition Audio CODEC while the Gene-Z has the higher end SupremeFX X-Fi 2 built-in 8-Channel High Definition Audio CODEC. The final difference and perhaps the easiest to spot is that the Extreme-Z is a full ATX board while the Gene-Z is uATX. Check out the performance of both boards in Legit Reviews latest article.

"The ASUS Maximus IV Extreme-Z is aimed at those looking to squeeze every last Megahertz out of their second generation Intel Core processor. With features like the LN2 switch that will help get past that pesky little cold bug problem, we know this board is meant for the extreme user. When we were performing our overclocking with the ASUS Maximus IV Extreme-Z it was a very smooth process. We were able to increase our multiplier to x51 and our Bclk to 100.4, though it showed up as 100.5 in CPUz. These settings brought us past the 5.1GHz mark and we were there in under an hour..."